1. Technical Field
The present invention relates generally to information storage systems and, more particularly, to a method and apparatus for improving a thermal response of a magnetoresistive (MR) element employed in an information storage system.
2. Description of the Prior Art
A typical data storage system includes a magnetic medium for storing data in magnetic form and a transducer used to write and read magnetic data respectively to and from the medium A disk storage device, for example, includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute. Digital information is typically stored in the form of magnetic transitions on a series of concentric, spaced tracks comprising the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a plurality of sectors, with each sector comprising a number of information fields, including fields for storing data, and sector identification and synchronization information, for example.
The actuator assembly typically includes a plurality of outwardly extending arms with one or more transducers and slider bodies being mounted on flexible suspensions. A slider body is typically designed as an aerodynamic lifting body that lifts the transducer head off of the surface of the disk as the rate of spindle motor rotation increases, and causes the head to hover above the disk on an air-bearing produced by high speed disk rotation. The distance between the head and the disk surface, typically on the order of 50-100 nanometers (nm), is commonly referred to as head-to-disk spacing.
Writing data to a data storage disk generally involves passing a current through the write element of the transducer assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the transducer assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface results in the production of electrical signals, commonly referred to as readback signals, in the read element.
Conventional data storage systems generally employ a closed-loop servo control system for positioning the read/write (R/W) transducers to specified storage locations on the data storage disk. During normal data storage system operation, a servo transducer, generally mounted proximate the read/write transducers, or, alternatively, incorporated as the read element of the transducer, is typically employed to read information for the purpose of following a specified track (track following) and locating (seeking) specified track and data sector locations on the disk.
Within the data storage system manufacturing industry, much attention is presently being focused on the use of a magnetoresistive (MR) element as a read transducer. As is well appreciated by those skilled in the art, the MR element provides a number of advantages over conventional thin-film heads and the like.
Several techniques have been developed to convert the magnetic signal induced in an MR element to a spacing signal that varies as a function of head-to-disk spacing changes. For example, the magnetic spacing signal has been used in defect screening procedures in an effort to detect the presence of anomalous disk surface features. Such surface defects are typically associated with excessively large head-to-disk spacing changes or disk surface contact events.
In order to conduct a survey of a disk surface using a magnetic spacing signal approach, magnetic information must first be written to the disk surface from which the magnetic spacing signal is subsequently produced. It is appreciated by those skilled in the art that writing magnetic information to a disk surface for purposes of conducting defect screening is a time consuming and costly process. Further, it is known that a magnetic spacing signal incorrectly indicates the presence of certain surface features, such as magnetic voids, as variations in the topography of a disk surface.
Fortunately, several techniques have been developed to convert the thermal response of an MR element to a spacing signal that varies as a function of head-to-disk spacing changes. In order to conduct a survey of a disk surface using a thermal spacing signal approach, magnetic information need not first be written to the disk surface. As a result, the thermal spacing signal approach reduces the cost and time currently expended using the magnetic spacing signal approach. For example, U.S. Pat. No. 5,527,110 to Abraham et al., which is assigned to the assignee of the present invention, discloses a method and apparatus for mapping the character and location of small surface variations on a disk surface using thermal proximity imaging. Energy is supplied to an MR element in close proximity to the planar surface of the disk to thereby raise the temperature of the MR element. Energy is supplied in the form of bias current flowing through the MR element. A change in temperature of the MR element is detected when the MR element is in proximity to the variation to define the location and character of the variation.
U.S. Pat. No. 5,527,110 teaches that further heating, i.e., in addition to that provided by bias current, can be supplied with a resistor, and in fact may be desirable to bias the magnetic sensitivity to near zero. However, the inventor of the present invention has found that the amount of further heating necessary to achieve a desired level of thermal response varies significantly both among nominally identical MR elements and over time in the same MR element. Thus it is difficult, if not impossible, to choose a single amount of further heating to provide to multiple MR elements or even one MR element over its lifetime. Moreover, the inventor of the present invention has found that further heating may introduce a head/disk contact problem. More specifically, further heating of the MR element may cause the transducer head to distend toward the surface of the disk, which increases the likelihood of head/disk contact. Contact between the transducer head and the disk surface may result in wearing of the magnetic film provided on the disk surface, thereby producing a magnetic void at the abraded disk surface location.
There exists a keenly felt need in the data storage system manufacturing community for an apparatus and method for improving the thermal response of an MR element. There exists a further need to provide an apparatus and method for improving the thermal response of an MR element without the above-discussed problems introduced by further heating. The present invention is directed to these and other needs.